You already learned that the grey line on the edit panel makes the replace line invisible. What do the other lines (yellow, purple, and green) do?

Try changing the first segment to each of the different color/types of lines (change the active segment type with the button below the drawing area, then click on the first line segment). For each color/type in the first segment, go to "Draw Mode" and go through a few iteration levels to see what the effect is. Experiment and record your observations.